1. Field of the Art
The present invention relates to a process for producing piperidine by liquid-phase catalytic hydrogenation of furfurylamine (FAM) and/or tetrahydrofurfurylamine (4H FAM). More specifically, the present invention relates to a process for preparing piperidine, characterized by the type of the catalyst used and by the manner in which the hydrogenation is carried out.
Piperidine is a useful compound as a starting material for pharmaceuticals, agricultural chemicals, rubber chemicals, and many other chemicals.
2. Prior Art
Hydrogenation of pyridine has been well known as a process for producing piperidine. However, a number of processes using materials other than pyridine have been proposed since pyridine is relatively expensive. Such processes comprise, for example, deammoniation-cyclization of 1,5-pentanediamine, ammonolysis of tetrahydropyran, 1,5-pentanediol or tetrahydrofurfuryl alcohol, and hydrogenation of FAM or 4H FAM. None of these processes can be made industrially practical because some starting materials used therein are not readily available or because some of these processes require high temperature reactions, result in a low yield, or are uneconomically complicated.
Among these processes, the process comprising hydrogenation of FAM or 4H FAM is expected to be an excellent industrial process if the hydrogenation can be conducted in a high yield because FAM can be produced in a high yield through reductive amination of furfural mass-produced from agricultural products, and also 4H FAM can be derived in a high yield through hydrogenation of the FAM.
It is reported in U.S. Pat. No. 2,265,201 that "a good yield of piperidine is obtained" (although no data is set forth) by adding to FAM liquid ammonia and a cobalt catalyst in an amount of 1/10 by weight of the raw material and subjecting the system to a batchwise hydrogenation reaction at 250.degree. C. under a pressure of 200 atm. for 10 hours. It is also reported that from 4H FAM "a good yield of piperidine is obtained" in a similar manner as in the case of FAM except that carbon monoxide is further added to the system. Furthermore, it is reported that a good yield of piperidine is produced under the conditions of a high temperature and a high pressure in the presence of ammonia over a copper chromite catalyst or a nickel catalyst. It is further reported that platinum catalyst may be used, and that the use of an inert solvent such as methanol or cyclohexane is advantageous in a liquid phase reaction, although the use of both of these catalysts is not supported by working examples.
Moreover, there are reported an example wherein piperidine is obtained in a yield of 9% from FAM without addition of ammonia by using Raney nickel as a catalyst and carrying out a reaction under a pressure of 100 atm. or higher [J. Am. Chem. Soc. Vol. 67, 693 (1945)], and an example wherein piperidine is obtained in a yield of 11% by using copper chromite catalyst [Acta. Chem. Scand. Vol. 20, 591 (1966)].
As described above, the prior art requires reaction conditions which are difficult to employ in commercial operation or results in a very low yield of the desired product. Thus, it can be said as far as we are aware that the prior process for catalytic hydrogenation of FAM and/or 4H FAM is still short of the level of industrial operations.